1. Field of the Invention
The present invention relates generally to optical attenuators, and more particularly, to an optical attenuator and a manufacturing method thereof, capable of controlling output light, using a micro electro mechanical system (referred to ‘MEMS’ hereinafter) technology and an electromagnetic force.
2. Description of the Related Art
Generally, an optical attenuator is an element that reduces an intensity of an optical power received at a receiving end of an optical communication system, thus preventing malfunction of the system.
The combination of a super highway network with a multimedia system, namely, a super highway information telecommunication service is realized on the basis of a wire or wireless super highway broadband communication technology. Particularly, as an important point of the wire technology, research has been conducted on an optical communication technology which deals with the transmission of broadband signals including picture signals as well as aural signals. Components constituting such an optical communication system are divided into active elements to constitute a light transmitting end of the system, and passive elements to control transmitted light in the system. Of the passive elements, a variable optical attenuator (VOA) that variably attenuates optical signals is commonly used.
The methods of attenuating light are classified as follows: 1) a method of attenuating light by inserting a thin-film filter made of metal, such as Cr, between optical fibers to absorb light; 2) a method of attenuating light by spacing optical fibers; 3) a method of attenuating light by splicing optical fibers so that the optical fibers cross each other; and 4) a method of attenuating light by adjusting the curvatures of optical fibers.
Recently, there has been manufactured an optical attenuator which blocks an optical path by driving a structure comprising a shutter or mirror by a micro-actuator, using the MEMS technology to meet a demand for the integration or miniaturization of an element. Further, in order to accomplish a multi-channel system, research has been conducted on applying a method of forming a waveguide using the Planar Lightwave Circuit (PLC) technology and changing a path of light which passes through the waveguide, to an optical attenuator.
FIGS. 1a and 1b are views to show a conventional PLC optical attenuator and operation of the attenuator, respectively.
FIG. 1a is a view to show an initial state of the conventional PLC optical attenuator. In the conventional PLC optical attenuator shown in FIG. 1a, optical waveguides 11, 12, and 13 are provided on a silicon substrate 10 to correspond to the MEMS structure, and the optical waveguides 11, 12, and 13 define a path to transmit optical signals. In the initial state of the optical attenuator, the optical waveguides 11, 12, and 13 are aligned in a row, and the optical signal is transmitted via the optical waveguides 11, 12, and 13.
FIG. 1b is a view to show the operation of the conventional PLC optical attenuator. Referring to FIG. 1b, the optical waveguides 11, 12, and 13 comprise an input waveguide 11, a movable waveguide 12, and an output waveguide 13. In an operated state, the movable waveguide 12 moves to be perpendicular to the optical path, so that an optical power is not fully transmitted from an input terminal to an output terminal. In this case, the optical power transmitted to the output terminal is varied, according to moving extent of the movable waveguide 12 relative to the input and output waveguides 11 and 13. In this way, the optical attenuator can attenuate a power of the optical signal. The movable waveguide 12 is coupled to an actuator (not shown) to be moved by driving the actuator.
When the conventional PLC optical attenuator is changed from the initial state to the operated state, the movable waveguide 12 moves to be perpendicular to the input and output waveguides 11 and 13 while being on a same plane with the input and output waveguides 11 and 13. However, the conventional PLC optical attenuator has a problem in that a space for the movement of the movable waveguide 12 and a space for installing the actuator coupled to the movable waveguide 12 are additionally required, so that a reduction in size of the optical attenuator is restricted. Further, when the conventional PLC optical attenuator is applied to each of multi-channel elements in order to control optical powers of the multi-channel elements having a plurality of optical paths, a larger space is required. Since the movable waveguide 12 is made of silica and arranged on the thin silicon substrate 10, the movable waveguide 12 and the silicon substrate 10 may be undesirably deformed due to a difference in stress between materials of the movable waveguide 12 and the silicon substrate 10. When the elements are deformed due to the difference in stress between the materials of the elements, it is difficult to obtain accurate attenuation characteristics.